linux-kernel - Re: [PATCH 1/3] mtd: nand: Add on-die ECC support

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Date:	Mon, 27 Apr 2015 16:10:02 -0700
From:	Brian Norris <computersforpeace@...il.com>
To:	Richard Weinberger <richard@....at>
Cc:	Ben Shelton <ben.shelton@...com>,
	"linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	David Woodhouse <dwmw2@...radead.org>,
	Punnaiah Choudary Kalluri 
	<punnaiah.choudary.kalluri@...inx.com>
Subject: Re: [PATCH 1/3] mtd: nand: Add on-die ECC support

On Mon, Apr 27, 2015 at 3:57 PM, Richard Weinberger <richard@....at> wrote:
> Am 28.04.2015 um 00:53 schrieb Brian Norris:
>> On Tue, Apr 28, 2015 at 12:42:18AM +0200, Richard Weinberger wrote:
>>> Am 28.04.2015 um 00:36 schrieb Ben Shelton:
>>>>>> When I build this without CONFIG_MTD_NAND_ECC_ON_DIE enabled, I get the
>>>>>> following warning here:
>>>>>>
>>>>>> In file included from drivers/mtd/nand/nand_base.c:46:0:
>>>>>> include/linux/mtd/nand_ondie.h: In function 'nand_read_subpage_on_die':
>>>>>> include/linux/mtd/nand_ondie.h:28:1: warning: no return statement in function returning non-void [-Wreturn-type]
>>>>>> include/linux/mtd/nand_ondie.h: In function 'nand_read_page_on_die':
>>>>>> include/linux/mtd/nand_ondie.h:34:1: warning: no return statement in function returning non-void [-Wreturn-type]
>>>>>>
>>>>>> Perhaps return an error code here, even though you'll never get past the BUG()?
>>>>>
>>>>> What gcc is this?
>>>>> gcc 4.8 here does not warn, I thought it is smart enough that this function does never
>>>>> return. Can it be that your .config has CONFIG_BUG=n?
>>>>> Anyway, this functions clearly needs a return statement. :)
>>>>
>>>> gcc 4.7.2, and you are correct that I had CONFIG_BUG off.  :)
>>>
>>> Yeah, just noticed that BUG() with CONFIG_BUG=n does not have
>>> a nonreturn attribute. So, gcc cannot know...
>>
>> But it's an obvious infinite loop... all of my toolchains (4.2, 4.5,
>> 4.6, 4.8) are able to compile this without complaining (gcc -Wall):
>>
>> int test() { do { } while (1); }
>
> Not here. gcc 4.8 warns on that.
> As soon I add __attribute__ ((noreturn)) it does not longer complain.

Huh? Maybe I have a crazy modified gcc.

$ gcc --version
gcc (Ubuntu 4.8.2-19ubuntu1) 4.8.2
Copyright (C) 2013 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ gcc -Wall -Wextra -c a.c
$ cat a.c
int test() { do {} while (1); }

But:

$ gcc -Wall -Wextra -c b.c
b.c: In function ‘test’:
b.c:1:1: warning: control reaches end of non-void function [-Wreturn-type]
 int test() { }
 ^
$ cat b.c
int test() { }
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